S1 atrioventricular valves close, S2 semilunar valves close, S3 rapid filling, S4 atrial contraction
Mnemonic
“S1 closes, S2 closes, S3 fills, S4 kicks”:
- S1 - mitral and tricuspid closing, at the start of systole
- S2 - aortic and pulmonary closing, at its end
- S3 - early diastole, rapid ventricular filling. “Ken-tuc-ky”
- S4 - late diastole, atrial contraction into a stiff ventricle. “Ten-nes-see”
S3 is normal under 30 and in pregnancy and athletes, but in older patients means a dilated, volume overloaded ventricle: heart failure, mitral regurgitation.
S4 is always abnormal and means a stiff, non-compliant ventricle: hypertension, aortic stenosis, hypertrophic cardiomyopathy, ischaemia. It cannot occur in atrial fibrillation, since it requires organised atrial contraction.
“S3 is a floppy ventricle, S4 is a stiff one.”
Expansion
- S1 - closure of the mitral and tricuspid valves, marking the start of systole
- S2 - closure of the aortic and pulmonary valves, marking the start of diastole
- S3 - early diastole, during rapid ventricular filling
- S4 - late diastole, during atrial contraction against a stiff ventricle
S3 is normal in children, athletes and pregnancy, where filling is brisk and the ventricle compliant. In an older patient it suggests volume overload, as in heart failure or mitral regurgitation, and gives a gallop cadence like the word “Ken-tuc-ky”.
S4 is always abnormal in adults and indicates a non-compliant ventricle, as in left ventricular hypertrophy, aortic stenosis or ischaemia; the cadence resembles “Ten-nes-see”. It cannot occur in atrial fibrillation, because it requires coordinated atrial contraction.